Window film is adhered to the outside of windows for many different reasons for example, the film may act as a safety film to prevent the shattering of glass when impacted. Another use of window film is solar control film which may reflect light at particular wavelengths or may absorb light of particular wavelengths. As is disclosed in U.S. Pat. No. 6,773,778, exterior window film typically comprises a base film or film laminate which is provided with a hard coat layer on its external surface.
The film surface to which the hard coat layer is applied may be subjected, if desired, to surface treatment by an oxidation method or a roughening method for the purpose of elevating the adhesive property with a layer provided on the surface thereof.
Exterior window film typically has a service life in the order of about 24 months and typically fails due to the loss of hard coat adhesion to the base substrate. When cycled in an Atlas Xenon Weatherometer according to ASTM G 155, a typical window film will fail in 600-900 hours due to loss of adhesion between the hard coat and the base film material when subjected to tape testing.
U.S. Pat. No. 6,787,236 describes a window film having a primer layer provided on one face of the base material with the hard coat applied over the primer layer. The primer layer is required to have a good adhesion with both the hard coat layer provided thereon and the base material. Conventionally known primers, are for example, primers of an acryl base, a polyester base, a polyurethane base, a silicone base and a rubber base.
The present invention provides for an exterior window film laminate with improved adhesion between the hard coat and the base material and which has improved resistance to the weather.